JP4820980B2 - PIN type circularly polarized light-emitting semiconductor element and laser element - Google Patents

Description

  The present invention provides a circularly polarized light-emitting semiconductor element capable of directly emitting left-handed circularly polarized light and right-handed circularly polarized light by modulating the degree of circular polarization (clockwise and counterclockwise) at high speed by an externally applied voltage, and The present invention relates to a circularly polarized light emitting laser element having a resonator structure.

  Currently, the development of optical technology that handles the polarization and phase of light is remarkable. The most common conventional method for obtaining circularly polarized light is a method of forming a circularly polarized state by passing light output from an external light source such as a light emitting diode or laser through a linear polarizer and a wave plate (λ / 4 plate). is there. However, in this method, the wave plate must be mechanically rotated to switch between the counterclockwise circular polarization state and the clockwise circular polarization state.

  Therefore, the modulation frequency for switching the circular polarization state is limited by the frequency of mechanical rotation of the wave plate, and there is a limit to speeding up the modulation (switching) of the circular polarization state. Moreover, the modulation frequency of the circularly polarized state by this method is only about several kHz or less, and modulation at higher speed cannot be expected.

  Another conventional method of modulating the circular polarization state at high speed is a method using a photoelastic modulator. In this method, light output from an external light source is passed through a linear polarizer and then incident on a photoelastic modulator. When an AC voltage (usually about 50 kHz) is applied to the photoelastic modulator, right-handed circularly polarized light and left-handed circularly polarized light appear alternately in the light transmitted through the photoelastic modulator in synchronization with the AC voltage.

  With this method, the modulation frequency of the degree of circular polarization (left-handed, right-handed) of the output light can be made higher than that of the conventional method described above, but it can only cause the right-handed circularly polarized light and the left-handed circularly polarized light to appear alternately. In principle, it is impossible to form clockwise circularly polarized light or counterclockwise circularly polarized light at an arbitrary timing.

  In addition, in any of the above conventional methods, in addition to the above problems, a plurality of optical elements (linear polarizer + wavelength plate, or linear polarizer + photoelastic modulator) are required outside. There is a limit to the miniaturization of devices and equipment. Furthermore, the optical element (device) is expensive, has a large light loss, and it is difficult to arrange a plurality of optical devices such as independent detectors or light sources and modulators adjacent to each other.

Against the background of such problems, a circularly polarized semiconductor laser combining a magnetic material and a semiconductor has been proposed as a light source that directly emits circularly polarized light (see Patent Documents 1 to 3).
Patent Document 1 discloses that “electrons or holes spin-polarized in an active region by providing a magnetic electrode on the upper or lower portion of a semiconductor element having a pn junction or a pin junction structure having an active region, or both. An optical semiconductor device "is disclosed.

  In the optical device using the above element, a conductor coil (external optical device) is overlaid on the magnetic electrode, and a current pulse is passed through the conductor coil to switch the magnetization direction of the magnetic electrode. The circularly polarized light is switched.

  Similarly, in Patent Documents 2 and 3, “an optical semiconductor that emits circularly polarized light by injecting spin-polarized electrons into a semiconductor layer forming a heterojunction through a magnetic layer and recombining spin-polarized carriers” An apparatus "is disclosed.

  In this optical semiconductor device, circularly polarized light is modulated by magnetization reversal of a magnetic material by an external magnetic field (external device).

  However, since any of the above circularly polarized light-emitting semiconductor elements uses modulation of an external magnetic field for modulation control of the degree of circular polarization, it is difficult to increase the modulation speed.

  Therefore, recently, an attempt has been proposed to apply a direct electric field to an optical semiconductor element to modulate and control the circular polarization state (see Non-Patent Documents 1 and 2). However, even in this proposal, the degree of circular polarization (clockwise, counterclockwise) is not controlled at high speed. In other words, no method has been proposed for directly modulating the circular polarization state (left-handed or clockwise) with an external electric field at high speed.

Japanese Patent No. 2770885 Japanese National Patent Publication No. 9-501266 US Pat. No. 5,874,749 Y. Ohno et al., “Electrical spin injection in a conjugated semiconductor heterostructure”, Nature 402 (1999) 790. R. Fiederling et al., “Injection and detection of a spin-polarized current in a light-emitting diode”, Nature 402 (1999) 787.

  In view of the fact that a method for directly controlling the circular polarization state with an external electric field at high speed has not been proposed, the present invention modulates the degree of circular polarization (clockwise and counterclockwise) at high speed with an externally applied voltage. An object of the present invention is to provide a circularly polarized light-emitting semiconductor element capable of outputting circularly polarized light, and a circularly polarized light-emitting laser element in which the structure of the element is configured as a resonator structure.

  As a result of intensive studies to achieve the above object, the present inventor has shown the exchange interaction between the spin of magnetic ions and the carrier spin in the semiconductor, which is manifested in a coupled quantum well structure composed of a ferromagnetic semiconductor and a nonmagnetic semiconductor. When used, it was found that the degree of circular polarization can be directly modulated by modulating the externally applied electric field.

  It has also been found that the modulation of the circular polarization degree can be speeded up by speeding up the modulation of the externally applied electric field.

  This invention was made | formed based on the said knowledge, and the summary is as follows.

(1) and the quantum well structure consisting of non-magnetic semiconductor layer, in contact next to the barrier layer of the structure, a band gap with a small magnetic semiconductor layer than the band gap of the barrier layer, the quantum well structure and the magnetic semiconductor layer And the carrier wave function in the quantum well layer of the non-magnetic semiconductor and the carrier wave function in the magnetic semiconductor layer are combined, and an externally applied electric field is applied to the up spin of the magnetic semiconductor layer. The voltage whose energy level matches the energy level of the valence band of the non-magnetic semiconductor layer forming the quantum well structure and the non-spin energy level of the magnetic semiconductor layer are By selecting and applying a voltage that matches the energy level of the valence band of the magnetic semiconductor layer, the upspin hole or the Dow stored in the magnetic semiconductor layer is reduced. The Nsupin holes, selectively implanted into the quantum well structure through the barrier layer, the result occurs (around the right, left-handed) circular polarization hole-electron recombination light emission, wherein Rukoto and can direct modulation A p-i-n type circularly polarized light-emitting semiconductor element.

( 2 ) The pin-type circularly polarized light-emitting semiconductor device according to (1 ), wherein the magnetic semiconductor layer is sandwiched between nonmagnetic semiconductor barrier layers to form a quantum well layer. .

( 3 ) The pin type circularly polarized light-emitting semiconductor device according to (1) or (2 ), wherein the magnetic semiconductor layer is a ferromagnetic semiconductor layer.

( 4 ) The pin according to any one of (1) to ( 3 ), wherein the nonmagnetic semiconductor is a group III-V nonmagnetic semiconductor or a group II-VI nonmagnetic semiconductor. Type circularly polarized light-emitting semiconductor element.

Above, wherein the a: (Al, either one or two of Ga A) (5) The group III-V magnetic _{semiconductor, A 1-x In x As} 1-y Sb y The pin type circularly polarized light-modulating light-emitting semiconductor element according to ( 4 ).

( 6 ) The group II- VI nonmagnetic semiconductor is AB (A: any one or more of Cd, Zn, Hg, B: any one of O, S, Se, Te) Or a p-i-n type circularly polarized light-emitting semiconductor element as described in ( 4 ) above.

( 7 ) The pin type circularly polarized light according to any one of (1) to ( 6 ), wherein the magnetic semiconductor is a group III-V magnetic semiconductor or a group II-VI magnetic semiconductor. Modulated light emitting semiconductor element.

( 8 ) The group III-V magnetic semiconductor is A _1-x B _x C (A: any one or more of Al, Ga, In, B: Sc, Ti, V, Cr, Mn , Fe, Co, or Ni, or one or more of C, N: P, As, or Sb), ( 7 ) The p-i-n type circularly polarized light-modulating light-emitting semiconductor element described in 1.

( 9 ) The II-VI group magnetic semiconductor is A _1-x B _x C (A: any one or two of Cd and Hg, B: Sc, Ti, V, Cr, Mn, Fe, Co, any one or two or more of Ni, C: O, S, Se, wherein characterized in that it is any one or more of Te) according to (7) p-i-n type circularly polarized light-emitting semiconductor element.

(1 0) and the quantum well structure consisting of non-magnetic semiconductor layer, in contact next to the barrier layer of the structure, a band gap with a small magnetic semiconductor layer than the band gap of the barrier layer, and comprises a resonator structure, The barrier layer separating the quantum well structure and the magnetic semiconductor layer is thin, and the wave function of carriers in the quantum well layer of the nonmagnetic semiconductor and the wave function of carriers in the magnetic semiconductor layer are combined, and an externally applied electric field The voltage at which the up spin energy level of the magnetic semiconductor layer matches the energy level of the valence band of the nonmagnetic semiconductor layer forming the quantum well structure, and the down spin energy level of the magnetic semiconductor layer is By selecting and applying a voltage that matches the energy level of the valence band of the non-magnetic semiconductor layer having the quantum well structure, the magnetic semiconductor layer can be stored. Up-spin holes or down-spin holes are selectively injected into the quantum well structure through the barrier layer, and the resulting circular polarization degree (right-handed, left-handed) of the electron-recombination light emission, direct modulation can p-i-n-type circularly polarized light modulating light emitting laser element characterized Rukoto.

(1 1) the magnetic semiconductor layer, p-i-n-type circularly polarized light modulating light emitting according to above, wherein the forming the quantum well layer sandwiched between barrier layers of non-magnetic semiconductor (1 0) Laser element.

(1 2 ) The pin circularly polarized light emitting laser element according to the above (1 0 ) or (11 ), wherein the magnetic semiconductor layer is a ferromagnetic semiconductor layer.

(1 3 ) The p− according to any one of (1 0 ) to (1 2 ), wherein the nonmagnetic semiconductor is a group III-V nonmagnetic semiconductor or a group II-VI nonmagnetic semiconductor. In type circularly polarized light emitting laser element.

(1 4) the group III-V magnetic _{semiconductor, A 1-x In x As} 1-y Sb y: characterized in that it is a (A Al, either one or two of Ga) The p-i-n type circularly polarized light-emitting laser element according to (1 3 ).

(1 5 ) The group II-VI nonmagnetic semiconductor is AB (A: any one or more of Cd, Zn, Hg, B: any one of O, S, Se, Te) The p-i-n type circularly polarized light emitting laser element according to (1 3 ), wherein the p-in type circularly polarized light-emitting laser element is a seed or two or more kinds.

( 16 ) The pin circle according to any one of (1 0 ) to ( 15 ), wherein the magnetic semiconductor is a group III-V magnetic semiconductor or a group II-VI magnetic semiconductor. Polarization modulation light emitting laser element.

( 17 ) The group III-V magnetic semiconductor is A _1-x B _x C (A: any one or more of Al, Ga, In, B: Sc, Ti, V, Cr, Mn , Fe, Co, or Ni, or one or more of C, N: P, As, or Sb), ( 16 ) The p-i-n type circularly polarized light-modulating light-emitting laser element described in 1.

( 18 ) The II-VI group magnetic semiconductor is A _1-x B _x C (A: any one or two of Cd and Hg, B: Sc, Ti, V, Cr, Mn, Fe, Co, any one or two or more of Ni, C: O, S, Se, wherein characterized in that it is any one or more of Te) according to (16) A p-i-n type circularly polarized light emitting laser element.

  In the circularly polarized light emitting semiconductor element and the circularly polarized light emitting laser element of the present invention, the modulation frequency of the degree of circular polarization reaches about 100 MHz for the circularly polarized light emitting element and about 10 GHz for the circularly polarized light emitting laser element. This modulation frequency is significantly higher than the modulation frequency (several kHz to several tens of kHz) possible with the prior art.

  Further, in the prior art, at least two external optical elements (linear polarizer + wavelength plate or linear polarizer + photoelastic modulator) are required to form a circular polarization state. Then, since the left and right polarization states can be formed without requiring such an external optical element (device), the optical device can be miniaturized and further integrated with another semiconductor.

  1) First, a circularly polarized light-emitting light-emitting semiconductor element will be described.

(1) Element Structure FIGS. 1A to 1D show four element structures characteristic of the circularly polarized light emitting semiconductor element and the circularly polarized light emitting laser element of the present invention (element of the present invention) and their energy levels. The coordinate structure is shown.

The element structure shown in FIGS. 1A and 1B includes a barrier layer A formed of a non-magnetic semiconductor having a large band gap, a quantum well layer B formed of a non-magnetic semiconductor having a small band gap, and a non-magnetic having a large band gap. It is composed of a barrier layer C formed of a semiconductor and a bulk layer D1 (energy is not quantized) formed of a magnetic semiconductor whose band gap is smaller than that of the barrier layer C.

In addition, the element structure shown in FIGS. 1C and 1D includes a barrier layer A formed of a nonmagnetic semiconductor having a large band gap, a quantum well layer B formed of a nonmagnetic semiconductor having a small band gap, and a large band gap. A barrier layer C formed of a nonmagnetic semiconductor, a quantum well layer D2 (energy is quantized) formed of a magnetic semiconductor whose band gap is smaller than that of the barrier layer C , and a nonmagnetic semiconductor having a large band gap The barrier layer E is formed.

  In FIG. 1, F to L indicate energy levels.

In the above four element structures, a quantum well structure including barrier layers A and C formed of a nonmagnetic semiconductor having a large band gap and a quantum well layer B formed of a nonmagnetic semiconductor having a small band gap; in contact next to the barrier layer, that it has a magnetic semiconductor layer D which band gap is formed in the lower magnetic semiconductor than the band gap of the barrier layer (bulk layer D1 or a quantum well layer D2) in common. This is a feature of the element of the present invention.

  Differences will be described below.

  In the element structure shown in FIGS. 1A and 1B, the magnetic semiconductor layer D is not sandwiched between barrier layers and does not form a quantum well layer. The layer D functions as the bulk layer D1.

  The element of the present invention utilizes the fact that the quantum level of the magnetic semiconductor causes energy splitting by up-spin and down-spin, but as described above, when the magnetic semiconductor does not form a quantization level In this case, it is used that the energy at the bottom of the valence band differs between upspin and downspin (see H and I in the figure).

  In the element structure shown in FIGS. 1C and 1D, the magnetic semiconductor layer D is sandwiched between barrier layers C and E to form a quantum well layer D2. In the quantum well layer D2, quantization levels (see K and L in the figure) are formed. That is, the magnetic semiconductor functions as a quantum well.

  Thus, when a magnetic semiconductor forms a quantized level, the splitting of the quantized level (see K and L in the figure) is used.

  In the element structure shown in FIGS. 1A and 1C, a barrier layer C (which separates a quantum well layer B formed of a nonmagnetic semiconductor and a magnetic semiconductor layer D (bulk layer D1 or quantum well layer D2) from each other. The non-magnetic semiconductor having a large band gap is formed thicker than the barrier layer C in the element structure shown in FIGS.

  When the barrier layer C is thick, there is no overlapping or coupling of wave functions in the quantum well layer and the magnetic semiconductor layer formed of a nonmagnetic semiconductor. On the other hand, when the thickness of the barrier layer C is thin, the wave functions are coupled in both layers.

(2) Operation Principle of Element Structure Here, the operation principle of the element of the present invention will be described by taking the element structure shown in FIG. FIG. 2A shows an example of the element of the present invention having the above element structure (an example of the element of the present invention), and FIGS. 2B and 2C show the energy level structure.

  In the element example of the present invention, layers A to E constituting the element structure shown in FIG. 1D are laminated on a substrate (n-type) Q via a buffer layer (n-type) R, and further non-magnetic. A contact layer S is stacked on the barrier layer E formed of a semiconductor (p-type). The A to E layers are configured so that a voltage V can be applied via the buffer layer (n-type) R and the contact layer S.

  In the quantum well layer D made of a p-type ferromagnetic semiconductor, the valence band undergoes energy splitting between the upward spin and the downward spin due to the exchange interaction between the spin of the magnetic ion and the carrier spin in the semiconductor ( (See I and J in the figure).

  The element example of the present invention is used below the Curie temperature of the ferromagnetic semiconductor constituting the quantum well layer D. According to previous reports, the Curie temperature is about 150 K or less, but in recent years, a ferromagnetic semiconductor having a higher Curie temperature (for example, room temperature or higher) has been reported. Since the ferromagnetic semiconductor used in the element of the present invention is not limited to a specific one, the operation of the element of the present invention is not necessarily limited only to a low temperature environment.

  In addition, since the ferromagnetic semiconductor has spontaneous magnetization below the Curie temperature, it is not necessary to apply an external magnetic field to the element in the operation of the element of the present invention, but in order to obtain a larger degree of circular polarization, During operation (or before operation), an external magnetic field may be applied as appropriate for magnetization.

  In the element example of the present invention shown in FIG. 2, the quantum well layer D has a smaller thickness than the quantum well layer B, and the quantization level (conduction band L, valence band I, J) is higher than the quantization level (conduction band M, valence band K) in the quantum well layer B.

  When a forward voltage V is applied to the element whose quantization level has the above relationship, electrons in the n-type region move in the direction of A → E in FIG. The hole moves in the direction of E → A, but the electrons are blocked by the central barrier layer C, so that they are accumulated in the quantum well layer B formed of an i-type nonmagnetic semiconductor, while the holes are p Is accumulated in the quantum well layer D formed of the type ferromagnetic semiconductor.

  Then, when a voltage (V = Va) is applied to the above element so that the quantization level K of the quantum well layer B matches the quantization level I of holes having an up spin in the quantum well layer D, Only holes having an up spin move to the quantum well layer B due to the resonant tunneling phenomenon, recombine in the quantum well layer B, and emit light (see FIG. 2B).

At this time, according to the optical selection rule, only electrons with up-spin and holes with up-spin are recombined, and emission of counterclockwise circularly polarized light (σ ⁻ ) is observed.

  Furthermore, when a voltage (V = Vb) is applied so that the quantization level K of the quantum well layer B and the quantization level J for holes having a down spin of the quantum well layer D coincide with each other, the down spin is obtained. Only holes are injected into the quantum well layer B by the resonant tunneling phenomenon, recombine, and emit light (see FIG. 2C).

At this time, according to the optical selection rule, only electrons with down spin and holes with down spin recombine, and light emission of clockwise circularly polarized light (σ ⁺ ) is observed.

Based on the above principle, by modulating the applied voltage between the voltages Va and Vb at a predetermined frequency, clockwise circularly polarized light (σ ⁺ ) and counterclockwise circularly polarized light (σ ⁻ ) can be modulated according to the frequency. This is a characteristic operation of the element of the present invention.

  (3) Here, semiconductor materials used in the element of the present invention will be described.

The p-type or n-type nonmagnetic semiconductor is preferably a group III-V nonmagnetic semiconductor or a group II-VI nonmagnetic semiconductor. In particular, as the group III-V magnetic _{semiconductor, A 1-x In x As} 1-y Sb y (A: Al, either one or two of Ga) is preferred, and, II -VI Group As the nonmagnetic semiconductor, AB (A: any one or more of Cd, Zn, Hg, B: any one or more of O, S, Se, Te) is preferable. .

As the p-type magnetic semiconductor, a III-V magnetic semiconductor is preferable. In particular, III-V group magnetic semiconductors include A _1-x B _x C (A: any one or more of Al, Ga, In, B: Sc, Ti, V, Cr, Mn, Any one or more of Fe, Co, and Ni, and any one or more of C: N, P, As, and Sb) are preferable.

  Further, the i-type magnetic semiconductor is preferably a group III-V magnetic semiconductor or a group II-VI magnetic semiconductor.

In particular, III-V group magnetic semiconductors include A _1-x B _x C (A: any one or more of Al, Ga, In, B: Sc, Ti, V, Cr, Mn, Any one or more of Fe, Co, and Ni, and any one or more of C: N, P, As, and Sb) are preferable.

In addition, as the II-VI group magnetic semiconductor, A _1-x B _x C (A: any one or two of Cd and Hg, B: Sc, Ti, V, Cr, Mn, Fe, Co , Any one or more of Ni, and any one or more of C: O, S, Se, and Te) are preferable.

  2) Next, a circularly polarized light emitting laser element will be described.

  The element structure of the circularly polarized light emitting laser element is basically the same as the element structure of the circularly polarized light emitting semiconductor element, and laser emission can be realized by making the structure into a resonator structure.

  The laser emission can be either a surface emission type or a stripe emission type, but in order to emit a laser having a larger degree of circular polarization, the element structure has a ferromagnetic semiconductor with in-plane magnetization. The case (for example, (Ga, Mn) As) is a stripe light emitting element structure (see FIGS. 3A and 3B), and the case where the ferromagnetic semiconductor has perpendicular magnetization (for example, (Ga , Mn) As: N) is preferably a surface-emitting element structure (see FIGS. 4A to 4C).

  Next, examples of the present invention will be described. The conditions of the examples are one example of conditions adopted for confirming the feasibility and effects of the present invention, and the present invention is limited to this one example of conditions. Is not to be done.

  The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

  Although some application examples are shown, the application of the element of the present invention is not limited to these application examples. The present invention can be applied in various ways as long as the characteristics (element structure and operation principle) are utilized.

Example 1 Fabrication of Circularly Polarized Modulated Light-Emitting Semiconductor Element Film Formation A film was formed on Si-doped n-type GaAs according to the following procedure using molecular beam epitaxy (MBE).

1. An Sn-doped n-GaAs layer (carrier concentration 5 × 10 ¹⁸ / cm ³ ) having a thickness of 2 μm was formed as a buffer layer at a substrate temperature of 600 ° C.

2. An Sn-doped n-Al _0.3 Ga _0.7 As layer (carrier concentration 5 × 10 ¹⁸ / cm ³ ) having a thickness of 50 nm was formed (barrier layer) at a substrate temperature of 600 ° C.

  3. A 4 nm thick non-doped GaAs layer is formed at a substrate temperature of 600 ° C. (quantum well layer).

4). A non-doped Al _0.3 Ga _0.7 As layer having a thickness of 5 nm was formed at a substrate temperature of 600 ° C. (barrier layer).

5). A ferromagnetic semiconductor (p-type) (Ga, Mn) As layer (Mn concentration 4%, carrier concentration 5 × 10 ¹⁹ / cm ³ ) with a substrate temperature of 210 ° C. is formed (quantum well layer).

6). A Be-doped p-AlGaAs layer (carrier concentration 5 × 10 ¹⁸ / cm ³ ) having a thickness of 20 nm was formed (barrier layer) at a substrate temperature of 210 ° C.

7). A Be-doped p-GaAs layer (carrier concentration 5 × 10 ¹⁹ / cm ³ ) having a thickness of 100 nm was formed at a substrate temperature of 210 ° C. (contact layer).

B. Processing The element structure produced by the MBE method was cleaved with the (110) plane as a cleavage plane. The element length (L) is 300 μm, and the width (W) is 200 μm. On top, Ti (5 nm) / Au (50 nm) was deposited as a p-electrode. After vapor deposition, the back surface of the n-GaAs substrate was mounted with In on the copper electrode of the IC holder. Furthermore, the p-electrode was connected to the terminal of the IC holder with a gold wire.

C. Detection of circularly polarized light output (C-1) Since the Curie temperature of the ferromagnetic semiconductor (Ga, Mn) As of the element was 100K, the element was cooled to a liquid nitrogen temperature (77K). Ferromagnetic semiconductors have spontaneous magnetization below the Curie temperature (the easy axis is in-plane), so there is no need to apply an external magnetic field to the device, but in order to obtain a greater degree of circular polarization, (Or before the operation), a permanent magnet for applying a magnetic field may be placed and magnetized by applying a magnetic field of about 0.55 Tesla.

  FIG. 5A shows the current / voltage characteristics, and FIG. 5B shows the applied voltage dependence of the output light intensity. It can be seen that extreme values appear at each of the applied voltages Va = 0.7V and Vb = 0.71V. As a result of measuring the wavelength of the output light using an optical spectrum analyzer, the wavelength was 770 nm.

  (C-2) Next, the degree of circular polarization of the output light was measured. FIG. 6 shows an apparatus arrangement configured to detect the degree of circular polarization of output light from a circularly polarized high-speed modulation light emitting semiconductor element.

  The output light is passed through a photoelastic modulator whose optical delay axis is inclined by 45 ° with respect to the horizontal plane (λ / 4 delay), and then passed through a Glan laser prism (linear polarizer) set at a polarization angle 0 with respect to the horizontal plane. The light intensity after linear polarization was received by a photodiode.

  The photoelastic modulator was adjusted by adjusting the applied voltage so that when linearly polarized light with a polarization angle of 0 was incident, clockwise and counterclockwise circularly polarized light was alternately generated at a frequency of 50 kHz.

The photocurrent generated from the photodiode was converted into a voltage signal and amplified by a current / voltage amplifier (amplification factor 10 ⁶ V / A) and then input to a digital storage oscilloscope (input impedance 100 MΩ).

FIG. 7 shows the waveform of the obtained output light. The degree of circular polarization P is defined by the following equation, where I ₊ and I ₋ are the intensity of clockwise circularly polarized light and counterclockwise circularly polarized light, respectively.

P = (I ₊ −I ₋ ) / (I ₊ + I ₋ )
FIG. 5C shows the applied voltage dependence of the degree of circular polarization. The circular polarization degree P is 20% at the maximum. Using this element, modulation was performed between counterclockwise circularly polarized light and clockwise circularly polarized light by making the current value constant and modulating the voltage between Va and Vb. In this device, the maximum modulation frequency of the degree of circular polarization was about 100 MHz.

Example 2 Fabrication of Circularly Polarized Modulated Light-Emitting Laser Element Film Formation A film was formed on Si-doped n-type GaAs according to the following procedure using molecular beam epitaxy (MBE).

1. A Sn-doped n-GaAs layer (carrier concentration 5 × 10 ¹⁸ / cm ³ ) having a thickness of 2 μm was formed as a buffer layer at a substrate temperature of 600 ° C.

2. An Sn-doped n-Al _0.3 Ga _0.7 As layer (carrier concentration 5 × 10 ¹⁸ / cm ³ ) having a thickness of 50 nm was formed at a substrate temperature of 600 ° C.

  3. A non-doped GaAs layer having a thickness of 5 nm is formed at a substrate temperature of 600 ° C.

4). A non-doped Al _0.3 Ga _0.7 As film having a thickness of 5 nm was formed at a substrate temperature of 600 ° C.

5). A ferromagnetic semiconductor (p-type) (Ga, Mn) As layer (carrier concentration 5 × 10 ¹⁹ / cm ³ ) having a thickness of 5 nm was formed at a substrate temperature of 210 ° C.

6). A Be-doped p-Al _0.3 Ga _0.7 As layer (carrier concentration 5 × 10 ¹⁸ / cm ³ ) having a thickness of 20 nm was formed at a substrate temperature of 210 ° C.

7). A 100-nm-thick Be-doped p-GaAs (carrier concentration 1 × 10 ¹⁹ / cm ³ ) was formed at a substrate temperature of 210 ° C.

B. Processing The upper part of the element structure manufactured by the MBE method was processed by photolithography to leave Al _0.3 Ga _0.7 As in a stripe shape. The stripe width (S) was 10 μm (see FIG. 3B). Thereafter, likewise using photolithography, on Al _0.3 Ga _0.7 As, a p-electrode was deposited Ti (5nm) / Au (20nm ).

The device structure was then cleaved along the (110) cleaved surface of GaAs. The element length (L) is 300 μm, and the width (W) is 200 μm. In order to increase the reflectance at the cleavage plane, a dielectric multilayer film in which ZnS and MgF ₂ were alternately laminated was deposited on the cleavage plane. In this device, the reflectance of the dielectric multilayer film at a transmission wavelength of 770 nm is about 98%.

  The p-electrode was connected to the terminal of the IC holder with a gold wire. Moreover, the back surface of the element structure was mounted with In on the copper electrode (n electrode) of the IC holder, and the n electrode was connected to the terminal of the IC socket with a gold wire.

C. Detection of Circularly Polarized Output FIG. 8 shows the result of measuring the wavelength of the output laser beam with an optical spectrum analyzer. Laser oscillation occurred when the forward applied voltage was 0.70V and 0.71V.

  FIG. 9 shows the forward current dependence of the laser output when the applied voltages are 0.70V and 0.71V. By modulating the applied voltage with a constant applied current, it was possible to modulate both the counterclockwise and right-handed circular polarization degrees. The maximum modulation frequency was about 10 GHz.

  As described above in (Example 1) and (Example 2), the element of the present invention actually functions as a circularly polarized light modulation optical semiconductor element. Therefore, various application examples of the element of the present invention can be considered, and typical application examples will be described below.

Application Example 1 Apparatus for Measuring the Abundance Ratio of Optical Isomers Using the element of the present invention, the above-described measuring apparatus as shown in FIG. 10 can be configured.

  Since optical isomers have the same physical and chemical properties other than optical rotation, in order to measure the abundance ratio of optical isomers, the difference in absorbance with respect to clockwise and counterclockwise circularly polarized light is detected. There is a need to. At this time, in order to measure the difference in the absorptance with high sensitivity, the method of detecting the modulation component of the light intensity transmitted through the optical isomer by high-speed modulation of the circular polarization degree of the output light is most useful ( Phase detection method).

  The element of the present invention can be applied to a measuring device according to the phase detection method because the degree of polarization of output light can be modulated at high speed by modulation of an externally applied voltage.

  In FIG. 10, one structure of the measuring apparatus which measures the abundance ratio of the optical isomer of L-glutamic acid aqueous solution is shown.

  The L-glutamic acid aqueous solution of the sample to be measured is irradiated with counterclockwise circularly polarized light and clockwise circularly polarized light. L-glutamic acid is an optical isomer and selectively absorbs left-handed circularly polarized light.

  Circularly polarized light that has passed through the sample to be measured is input to a photodiode, the output current is amplified by a current / voltage conversion amplifier, and input to a digital oscilloscope.

  Since the L-glutamic acid aqueous solution of the sample to be measured shows circular dichroism of 100 mdeg by another measurement, the circular dichroism of the sample to be measured is calculated by a personal computer (not shown). Check for consistency. In one calculation example, a circular dichroism of about 100 deg was obtained. Thus, by using the element of the present invention, the circular dichroism of optical isomerism can be measured with high accuracy.

Application Example 2 Ellipsometry Device The element of the present invention can be applied to an ellipsometry device (see FIG. 11). In the ellipsometry apparatus, light from a light source is linearly polarized by a linear polarizer, incident on a sample obliquely, and the ellipticity of the reflected light is measured. In this method, at least three external optical elements ( Device) (see FIG. 11A), there is a limit to downsizing the entire apparatus.

  However, when the element of the present invention is used, as shown in FIG. 11B, the required optical element (equipment) is one linear polarizer, so that the entire apparatus can be greatly reduced in size.

(Application example 3) Light source for high-speed optical communication In an existing optical communication network, communication is performed with the intensity of light corresponding to 0 or 1 of a signal. In order to realize communication multiplexing, it is conceivable to use the degree of freedom of polarization. However, in the conventional technology, the degree of clockwise and counterclockwise circular polarization must be controlled by an external optical element (equipment). It is difficult to reduce the size of the light source and to increase the speed.

  Since the present invention element can modulate right-handed circularly polarized light and left-handed circularly polarized light at high speed by modulating the external voltage at high speed, it can be multiplexed in an existing optical communication network by using the present invention element as a light source. High-speed communication can be achieved.

(Application Example 4) Observation of magnetic domain structure of nanostructured magnetic memory Since the reflectivity differs between the left-handed circularly polarized light and the right-handed circularly polarized light according to the direction of the perpendicular magnetization of the sample surface, magnetic random access memory (MRAM), etc. It can be used as a small light source for directly observing the magnetic domain structure on the surface of the substrate.

  According to the present invention, the degree of clockwise and counterclockwise circular polarization can be controlled at high speed by an externally applied voltage. That is, the frequency of the externally applied voltage can be modulated and the degree of polarization of the output light can be modulated and controlled at high speed.

  Further, since the present invention does not require an external optical element (device), the optical device can be miniaturized and can be further integrated with a semiconductor.

  Therefore, the present invention has extremely high applicability not only in optical technology but also in advanced technology industries based on production technology, information communication technology, spectroscopy, nanotechnology, and quantum manipulation technology.

It is a figure which shows the element structure of this invention element, and its energy level structure. It is a figure which shows the example of this invention element based on the element structure shown in FIG.1 (d). (A) shows the element structure, and (b) and (c) show the principle of operation. ) Shows the element structure, and (b) and (c) show the principle of operation. It is a figure which shows an example of the stripe light emission type laser element (The ferromagnetic semiconductor has magnetized in the surface) of this invention. It is a figure which shows the other example of the stripe light emission type laser element (The ferromagnetic semiconductor is magnetized in a surface) of this invention. It is a figure which shows an example of the surface emitting laser element (the ferromagnetic semiconductor is perpendicularly magnetized) of this invention. It is a figure which shows the other example of the surface emitting laser element (the ferromagnetic semiconductor is perpendicularly magnetized) of this invention. It is a figure which shows the upper surface of the surface emitting type laser element (The ferromagnetic semiconductor is perpendicularly magnetized) of this invention. It is a figure which shows the special current and voltage characteristic of this invention. It is a figure which shows the applied voltage dependence of the output light intensity of this invention. It is a figure which shows the applied voltage dependence of the circular polarization degree of this invention. It is a figure which shows the example of an apparatus arrangement | sequence which detects a circular polarization degree. It is a figure which shows the waveform of output light. It is a figure which shows the result of having measured the wavelength of the output laser beam with the optical spectrum analyzer. It is a figure which shows the forward current dependence of a laser output. It is a figure which shows the structural example of the measuring apparatus of the abundance ratio of the optical isomer which used this invention element. It is a figure which shows the structural example of an ellipsometry apparatus. (A) shows the example of a conventional structure, (b) shows the example of a structure using this invention element.

Explanation of symbols

A barrier layer (layer formed of non-magnetic semiconductor with large band gap)
B Quantum well layer (layer formed of non-magnetic semiconductor with small band gap)
C barrier layer (layer formed of non-magnetic semiconductor with large band gap)
D Magnetic semiconductor layer (a layer formed of a magnetic semiconductor having a small band gap)
D1 bulk layer (energy is not quantized)
D2 quantum well layer (energy is quantized)
E barrier layer (layer formed of non-magnetic semiconductor with large band gap)
F to M Energy level Q Substrate (n-type)
R buffer layer (n-type)
S contact layer

Claims (18)

A quantum well structure comprising a nonmagnetic semiconductor layer; and a magnetic semiconductor layer having a band gap smaller than that of the barrier layer adjacent to the barrier layer of the structure, and separating the quantum well structure from the magnetic semiconductor layer. The barrier layer is thin, the carrier wave function in the quantum well layer of the nonmagnetic semiconductor and the carrier wave function in the magnetic semiconductor layer are combined, and the externally applied electric field is applied to the up spin energy level of the magnetic semiconductor layer. The voltage that matches the energy level of the valence band of the nonmagnetic semiconductor layer that forms the quantum well structure and the down spin energy level of the magnetic semiconductor layer form the nonmagnetic semiconductor layer that forms the quantum well structure. valence voltage matching the energy level of the valence band by applying by selecting, up-spin holes or Daunsupi stored in the magnetic semiconductor layer P of the hole, then selectively implanted into the quantum well structure through the barrier layer, resulting occur circular polarization hole-electron recombination light emission (around the right, counter-clockwise), characterized in that the, can be modulated directly -In type circularly polarized light-emitting semiconductor element. 2. The pin type circularly polarized light-emitting semiconductor device according to claim 1, wherein the magnetic semiconductor layer is sandwiched between nonmagnetic semiconductor barrier layers to form a quantum well layer. The magnetic semiconductor layer, p-i-n-type circularly polarized light modulating light emitting semiconductor device according to claim 1 or 2, characterized in that a ferromagnetic semiconductor layer. The pin type circularly polarized light modulation according to any one of claims 1 to 3 , wherein the nonmagnetic semiconductor is a group III-V nonmagnetic semiconductor or a group II-VI nonmagnetic semiconductor. Light emitting semiconductor element. The group III-V magnetic _{semiconductor, A 1-x In x As} 1-y Sb y: to claim 4, characterized in that the (A Al, either one or two of Ga) The p-i-n type circularly polarized light-modulating light-emitting semiconductor element described. The II-VI group nonmagnetic semiconductor is AB (A: any one or more of Cd, Zn, Hg, B: any one or two of O, S, Se, Te) The pin-type circularly polarized light-modulating light-emitting semiconductor element according to claim 4 , wherein: Wherein the magnetic semiconductor is, III-V group magnetic semiconductor or a group II-VI p-i-n-type circularly polarized light modulating light emitting semiconductor device according to any one of claims 1 to 6, characterized in that a magnetic semiconductor . The group III-V magnetic semiconductor is A _1-x B _x C (A: any one or more of Al, Ga, In, B: Sc, Ti, V, Cr, Mn, Fe, Co, Ni or one or more of, C: N, P, as , p according to claim 7, characterized in that any one or more) of Sb -In type circularly polarized light-emitting semiconductor element. The II-VI group magnetic semiconductor is A _1-x B _x C (A: any one or two of Cd and Hg, B: Sc, Ti, V, Cr, Mn, Fe, Co, Ni any one or more of, C: O, S, Se , according to claim 7, characterized in that any one or more) of the Te p-i- n-type circularly polarized light-emitting semiconductor element. A quantum well structure comprising a non-magnetic semiconductor layer; a magnetic semiconductor layer having a band gap smaller than that of the barrier layer adjacent to the barrier layer of the structure; and a resonator structure, the quantum well structure a magnetic semiconductor layer above the barrier layer is thin separating, and wave functions of the carriers in the non-magnetic semiconductor quantum well layer, be bonded wave functions of the carriers in the magnetic semiconductor layer, an externally applied electric field, the magnetic The voltage at which the up spin energy level of the semiconductor layer matches the energy level of the valence band of the nonmagnetic semiconductor layer forming the quantum well structure, and the down spin energy level of the magnetic semiconductor layer by applying selected voltages to match the energy level of the valence band of the non-magnetic semiconductor layer constituting the structure, up stored in the magnetic semiconductor layer Pins holes or down spin hole, the through barrier layer selectively implanted into the quantum well structure, resulting occur circular polarization hole-electron recombination light-emitting (about right, counterclockwise) the direct modulation A p-i-n type circularly polarized light emitting laser element characterized by being capable of being produced. The magnetic semiconductor layer, p-i-n-type circularly polarized light modulating light emitting laser device according to claim 1 0, characterized in that to form a quantum well layer sandwiched between barrier layers of non-magnetic semiconductor. The magnetic semiconductor layer, p-i-n-type circularly polarized light modulating light emitting laser device according to claim 1 0 or 11, characterized in that the ferromagnetic semiconductor layer. The non-magnetic semiconductor, p-i-n type circular according to any one of claims 1 0 to 1 2, which is a group III-V magnetic semiconductor or a II-VI nonmagnetic semiconductor Polarization modulation light emitting laser element. The group III-V magnetic _{semiconductor, A 1-x In x As} 1-y Sb y: claims 1 to 3, characterized in that the (A Al, either one or two of Ga) The p-i-n type circularly polarized light-modulating light-emitting laser element described in 1. The II-VI group nonmagnetic semiconductor is AB (A: any one or more of Cd, Zn, Hg, B: any one or two of O, S, Se, Te) p-i-n-type circularly polarized light modulating light emitting laser device according to claim 1 3, characterized in that the higher). Wherein the magnetic semiconductor is, III-V group magnetic semiconductor or a group II-VI p-i-n-type circularly polarized light modulating light emitting laser according to any one of claims 1 0-15, characterized in that a magnetic semiconductor element. The group III-V magnetic semiconductor is A _1-x B _x C (A: any one or more of Al, Ga, In, B: Sc, Ti, V, Cr, Mn, Fe, The p according to claim 16 , which is any one or more of Co and Ni and any one or more of C: N, P, As, and Sb). -In type circularly polarized light emitting laser element. The II-VI group magnetic semiconductor is A _1-x B _x C (A: any one or two of Cd and Hg, B: Sc, Ti, V, Cr, Mn, Fe, Co, Ni any one or more of, C: O, S, Se , according to claim 16, characterized in that any one or more) of the Te p-i- An n-type circularly polarized light emitting laser element.

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